It is known that a stack of sheets, when the sheets are delivered by high-output presses, grows rapidly, especially when relatively thick materials such as cartons are being used. However, since the stacker has a limited capacity, the stack has to be changed more than once during the printing of a run. To enable the press to run with a very high output despite stack-changing, intermediate stackers have been devised. These stackers are used for stack-changing while the press continues to run and serve to provisionally stack the printed sheets during stack-changing. The present invention relates to an improvement in a device such as disclosed in DE-PS No. 31 12 672, which is the priority application for U.S. Pat. No. 4,452,442 to Geschwindner et al., the details of which are incorporated herein by reference. In brief summary, in such a device, when sheets are deposited on a vertically lowerable intermediate stacker, the rear edge of the sheets are aligned so that no edge displacement can occur when the stack is transferred to the main stack. A sheet stop is in the form of a cross-member and is pivotally connected by a link parallelogram support to the sheet brake, thus extending the lift of the intermediate stacker.
A disadvantage in such a device is that it becomes difficult to build a stack with the edges properly adjusted when sheets of different sizes are present. When the cross-member type stop is adjusted to the shortest sheet, there is a risk of longer sheets sticking, thereby raising the possibility that disturbances to non-stop operation may result. Yet when the stop is adjusted to accommodate the longest sheet which, for example, is 3 mm longer than the shortest one, the stack edges become untidy and inaccurate. This may lead to disturbing differences in contact in further processing in automatic punching machines or the like.
According to DE-OS No. 31 127 540, aligning devices for sheet deliveries of printing presses have stationary and moving sheet stops, in which the moving stops consist of brushes having soft bristles. However, this publication does not disclose an intermediate stacker which can be raised and lowered to form a relatively large stack and, more particularly, which is of use for dealing with thick carton material. Another disadvantage is that due to the presence of the brushes on both sides of the delivered sheets, the relative alignment of the front edge is bound to be uncertain because of lateral recoil of the bristles caused by previously deposited sheets. Also, the sheet may be impeded on both sides from dropping through freely. Yet another disadvantage is the costly drive needed to rotate the laterally positioned brushes.